Wellhead seals are used to seal across the annular space between the exterior of a hanger and the interior of a wellhead housing in which the hanger is supported. Many types of seals have been used in the past. Such seals have included resilient annular members which are positioned within the annular space and compressed axially to expand them into sealing engagement with the surfaces defining the interior and exterior of the annular space, such as disclosed in U.S. Pat. No. 3,797,864.
Other seals include metal members having lips urged into engagement with the inner and outer sealing surfaces as shown in U.S. Pat. Nos. 2,405,152; 2,746,486; 4,131,287; and 4,178,020.
Some seals have utilized a combination of resilient and metal seals such as illustrated by U.S. Pat. Nos. 4,488,740 and 4,550,782.
Additionally seals have been provided which utilize a resilient or metal seal which is mechanically wedged or cammed into sealing engagement with the walls of the annular space in a well bore. Other seal structures have included threaded or roughened sealing surfaces, such as wickers, which provide a positive metal-to-metal seal. U.S. Pat. No. 4,595,053 is an example of these two types of seals.